1. Field of the Invention
The present invention relates to a rotational angle detecting apparatus for detecting an rotational angle of a rotor, a torque sensor using the rotational angle detecting apparatus, and a steering apparatus for generating steering assistance force by driving an electric motor based on the result of the detection of the torque sensor.
2. Description of Related Art
Some steering apparatus for automobiles assist steering by driving electric motors thereof, so as to lighten drivers"" load. A steering apparatus comprises an input shaft connected to a steering wheel, an output shaft connected to wheels for steering through a pinion and a rack, for example, and a torsion bar which connects the input shaft and the output shaft. A steering torque applied to the input shaft is detected as torsion generated on the torsion bar by a torque sensor. An electric motor for steering assistance, which interlocks with the output shaft, is driven and controlled based on the detected steering torque.
In an essential structure example of a rotational angle detecting apparatus and a torque sensor based on Patent Application Laid-Open No.2000-352502 proposed by the present applicant, a steering shaft is connected to a steering wheel 4 at an upper end thereof and to a torsion bar 5 at a lower end thereof as shown in FIG. 1. An upper shaft 23 of the steering shaft has a plurality of (FIG. 1 shows ten) protruding objects 7, 7 . . . made of magnetic material, with a predetermined tilt angle and along a circumferential surface of an intermediate portion 6 thereof. When the upper shaft 23 rotates, the protruding object 7 moves in an axial direction of the upper shaft 23. For detecting an adjacent part of the protruding object 7 moving in an axial direction of the upper shaft 23, a MR sensor 1 (a magneto-resistance effect element) is fixed to an immovable portion of the automobile body, having an appropriate space with and being parallel to the intermediate portion 6.
A lower shaft 18 of the steering shaft is connected to the torsion bar 5 at an upper end thereof and to a pinion 10 at a lower end thereof. The lower shaft 18, similarly with the upper shaft 23, has a plurality of (FIG. 1 shows ten) protruding objects 9, 9 . . . made of magnetic material, with a predetermined tilt angle and along a circumferential surface of an intermediate portion 8 thereof. When the lower shaft 18 rotates, the protruding object 9 moves in an axial direction of the lower shaft 18. For detecting an adjacent part of the protruding object 9 moving in an axial direction of the lower shaft 18, a MR sensor 2 (a magneto-resistance effect element) is fixed to an immovable portion of the automobile body, having an appropriate space with and being parallel to the intermediate portion 8.
The MR sensor 1 has sensors 1A and 1B, which have 180xc2x0 different electrical angles, at the interior thereof. Detected signals V1A and V1B indicating the part of the protruding object 7, which are detected by the sensors 1A and 1B, are respectively given to a signal processing unit 11. The signal processing unit 11 detects a rotational angle of the upper shaft 23 based on the detected signals V1A and V1B. A rotational angle detecting apparatus of the upper shaft 23 is thus constructed from the sensors 1A, 1B and the signal processing unit 11.
The MR sensor 2 has sensors 2A and 2B, which have 180xc2x0 different electrical angles, at the interior thereof. Detected signals V2A and V2B indicating the part of the protruding object 9, which are detected by the sensors 2A and 2B, are respectively given to a signal processing unit 11. The signal processing unit 11 detects a rotational angle of the lower shaft 18 based on the detected signals V2A and V2B. A rotational angle detecting apparatus of the lower shaft 18 is thus constructed from the sensors 2A, 2B and the signal processing unit 11.
The MR sensors 1 and 2 are provided in a condition where the detected signals V1A and V2A (output of sensor) are at the same phase and the detected signals V1B and V2B (output of sensor) are at the same phase as shown in FIG. 3 when no steering torque is applied to the steering wheel 4 and the torsion bar 5 is not twisted.
A torsion angle of the torsion bar 5 is several degrees at the utmost. The signal processing unit 11 calculates a steering torque based on difference between the rotational angle of the upper shaft 23 obtained from a detected signal V1A or V1B and the rotational angle of the lower shaft 18 obtained from a detected signal V2A or V2B, and outputs a torque signal.
In a torque sensor constructed as described above, every 36xc2x0 the upper shaft 23 and the lower shaft 18 rotate, each part of the protruding object 7 and the protruding object 9 where is most adjacent to each detecting surface of the sensors 1A, 1B and the sensors 2A, 2B makes a return trip in axial direction of the upper shaft 23 and the lower shaft 18. The position in axial direction of the upper shaft 23 and the lower shaft 18 of each part of the protruding object 7 and the protruding object 9 where is most adjacent to each detecting surface of the sensors 1A, 1B and the sensors 2A, 2B corresponds to the rotational angle of the upper shaft 23 and the lower shaft 18.
In practice, the above-mentioned program for calculating each rotational angle of the upper shaft 23 and the lower shaft 18 is omitted. When a steering torque is applied to the steering wheel 4 and the torsion bar 5 is twisted, voltage difference xcex94V corresponding to the torsion angle arises between each detected signal of sensors 1A and 2A, and each detected signal of sensors 1B and 2B. The torsion angle is obtained by calculating the voltage difference xcex94V at the signal processing unit 11. The signal processing unit 11 outputs the torque signal expressing the steering torque.
However the above-mentioned rotational angle detecting apparatus and the torque sensor do not have means for detecting malfunction of the sensors 1A, 1B, 2A, and 2B when malfunction occurs. Consequently when the rotational angle detecting apparatus and the torque sensor fail, a torque is calculated based on erroneous detected signals, and an erroneous torque signal is outputted.
The present invention has been made with the aim of solving the above problem.
It is an object of the invention to provide a rotational angle detecting apparatus which can detect malfunction.
Another object of the invention is to provide a torque sensor comprising the rotational angle detecting apparatus.
A further object of the present invention is to provide a steering apparatus comprising the torque sensor.
In a rotational angle detecting apparatus according to the first invention, one or a plurality of targets are arranged on a rotor, to output signals which repeat periodical increase and decrease in accordance with rotation of the rotor. First detecting means detects an adjacent part of the target. Second detecting means detects a part, which is a predetermined angle distant in a circumferential direction of the rotor from the part detected by the first detecting means. The rotational angle of the rotor is detected based on a detected signal which is outputted from the first detecting means or the second detecting means. A memory stores pairs of detected signal values which the first detecting means and the second detecting means should output synchronously. Judging means judges whether a pair of detected signal values, which is approximately the same as a pair of detected signal values outputted from the first detecting means and the second detecting means synchronously, is included in the pairs of detected signal values stored in the memory. When the judging means judges in the negative, a malfunction indicating signal is outputted.
Consequently the above-mentioned rotational angle detecting apparatus can detect malfunction, and more particularly, can detect the malfunction thereof even when the broken rotational angle detecting apparatus outputs a detected signal which is within a range.
In a rotational angle detecting apparatus according to the second invention, one or a plurality of targets are arranged on a rotor, to output signals which repeat periodical increase and decrease in accordance with rotation of the rotor. First detecting means detects an adjacent part of the target. Second detecting means detects a part, which is a predetermined angle distant in a circumferential direction of the rotor from the part detected by the first detecting means. The rotational angle of the rotor is detected based on a detected signal which is outputted from the first detecting means or the second detecting means. Selecting means selects the first detecting means or the second detecting means for detecting the rotational angle of the rotor. A memory stores, corresponding to a detected signal value which should be outputted from one of the detecting means which is selected by the selecting means, a detected signal value which should be synchronously outputted from the other detecting means. Judging means judges whether the detected signal value of the other detecting means, which the memory stores corresponding to the detected signal value outputted from the one of the detecting means selected by the selecting means, is approximately the same as a detected signal value outputted from the other detecting means. When the judging means judges in the negative, a malfunction indicating signal is outputted.
Consequently the above-mentioned rotational angle detecting apparatus can detect malfunction, and more particularly, can detect the malfunction thereof even when the broken rotational angle detecting apparatus outputs a detected signal which is within a range.
A torque sensor according to the present invention comprises a rotational angle detecting apparatus according to the first invention or the second invention at an input shaft and an output shaft respectively, the input shaft and the output shaft being connected by a torsion bar. The torque sensor detects a torque applied to the input shaft based on rotational angle difference, which is generated by a torsion of the torsion bar, detected by the rotational angle detecting apparatus.
The above-mentioned torque sensor can detects malfunction of the rotational angle detecting apparatus.
In a steering apparatus according to the present invention, an input shaft is connected to a steering wheel and an electric motor for steering assistance is driven and controlled based on a steering torque applied to the steering wheel. An output shaft interlocks with the electric motor, a torsion bar connects the input shaft and the output shaft, the torque sensor according to the present invention detects a steering torque applied to the input shaft, and steering is assisted based on a steering torque detected by the torque sensor.
The above-mentioned steering apparatus comprises the torque sensor which can detects malfunction of the rotational angle detecting apparatus.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.